Showing papers on "Silica gel published in 1982"

Cross-polarization magic-angle-spinning silicon-29 nuclear magnetic resonance study of silica gel using trimethylsilane bonding as a probe of surface geometry and reactivity

Abstract: /sup 29/Si NMR experiments, using cross polarization (CP) and magic-angle spinning (MAS), were carried out on a variety of silica gels and the products of their trimethylsilylation reactions with the silylating agent, hexamethyldisilazane (HMDS). A methodology has been developed to provide quantitative relationships on structure and reactivity from the /sup 29/Si CP/MAS spectra. Geminal-hydroxyl silanol sites were found to be more reactive to HMDS than lone-hydroxyl silanol sites. Measured surface hydroxyl densities and trimethylsilane coverages are discussed in terms of structural models.

Properties and diversity of C18 bonded phases

Abstract: The effect of the properties of the silica gel matrix, and of the octadecylsilane used, on the chromatographic selectivity of C18 bonded phases is described. Preparation of bonded phases with monochlorodimethyloctadecylsilane is easier because absolute water exclusion is not required in this case. The surface coverage (μmol/m2) is smaller than with dichloromethyl- or trichlorooctadecylsilanes, but in these cases a secondary silanization with HMDS is essential to remove newly formed silanol groups. Bonded phases on Si 60 give the largest amount of hydrocarbon per unit column volume, large k′ values and good selectivity, however, surface coverage and efficiency of these packed columns is less than with Si 100 silica. The chemical properties of the silica surface also influence bonded phase selectivity. Bonded phases should not be compared with only a single eluent, because properties of bonded phases differ with test solutes and test conditions, i.e. eluent composition.

Direct separation of amino enantiomers by high performance ligand exchange chromatography on chemically bonded chiral phases

Abstract: Various chiral chemically bonded stationary phases for the separation of amino acid enantiomers by high performance ligand exchange chromatography are described. The phases were synthesized by treating silica gel with 3-glycidoxypropyltrimethoxysilane and bonding L-amino acids such as L-azetidine carboxylic acid, L-pipecolic acid or L-phenylalanine to the product. The best results were obtained with L-pipecolic acid as a fixed ligand. Nearly all common amino acid enantiomers could be separated.

Preparation of monolithic silica aerogels, the aerogels thus obtained and their use for the preparation of silica glass articles and of heat-insulating materials

Abstract: The invention relates to a process for the preparation of monolithic silica aerogels by drying silica gels under hypercritical conditions, which is characterized by the absence of washing of the silica gel, a high heating rate in the autoclave and purging of the autoclave after substantial removal of the solvent. Other preferred conditions are the use of an amount of water not exceeding 1.5 times the stoichiometric amount for the hydrolysis, hypercritical conditions corresponding to a temperature of 265°-275° C. and to a pressure of 150-200 bars, and so on. Use of the aerogels for the preparation of silica glass bodies or articles and of heat-insulating materials.

Silica sol compositions for polishing silicon wafers

Abstract: Semi-conductors can be polished with greater efficiency using as a polishing agent a blend of colloidal silica or silica gel, a water-soluble amine and a water-soluble quaternary ammonium salt or base.

Fixation by anion exchange of toxic materials in a glass matrix

Abstract: This invention relates to the immobilization of toxic, e.g., radioactive, materials in a silicate glass or silica gel matrix for extremely long periods of time. Toxic materials, such as radioactive wastes containing radioactive cations, which may be in the form of liquids, or solids dissolved or dispersed in liquids or gases, are incorporated into a glass or silica gel matrix, having alkali metal, Group Ib metal and/or ammonium cations bonded to silicon atoms of said glass or silica gel through divalent oxygen linkages, by a process which involves the ion exchange of said toxic or radioactive cations with said alkali metal, Group Ib metal and/or ammonium cations to bind said toxic or radioactive cations to silicon atoms of said glass or silica gel through said silicon-bonded divalent oxygen linkages. Thereafter, the resulting glass or silica gel now characterized by toxic or radioactive cations bonded to silicon atoms through divalent oxygen linkages can be stored, or packaged in suitable containers, or disposed of as by burial, and/or sintered to collapse the pores thereof.

Fourier transform infrared spectrometry, carbon-13 nuclear magnetic resonance spectrometry, and photoacoustic spectroscopy of a silica-immobilized ligand

Abstract: Infrared spectometry, ultraviolet absorbance spectrometry, photoacoustic spectroscopy, and solid-state /sup 13/C NMR spectrometry have in combination produced useful information about an immobilized acetoacetamide. The immobilized acetoacetamide formed by reacting diketene with either aminopropylsilane or (aminoethyl)aminopropylsilane bound to silica gel is strongly hydrogen bonded and largely in the keto form. The keto form can be converted to the enolate ion only in very alkaline conditions. In weakly acidic solutions the keto form complexes with several metal ions.

Sorbed Uranium (VI) Species on Hydrous Titania, Zirconia, and Silica Gel

Abstract: The solids resulting from the sorption of uranium(VI)-carbonate complexes on hydrous titania, zirconia, and silica gel were examined by Raman spectroscopy, scanning electron microscopy, and direct analytical methods. It has been established that the sorption process involves the displacement of the carbonate ligands from the soluble species and yields a uranyl moiety, free of carbonate, that is strongly bound to the substrate. The bonding interaction with the solids involves considerable electron density transfer to the uranyl moiety character ; this is evidenced by the shifts in the υ, -UO, stretching frequency of the sorbed species as compared with that of the U O | + ion.

Synthesis and characterization of silica gel ion-exchanger bearing 2-amino-1-cyclopentene-1-dithio-carboxylic acid (ACDA) as chelating compound

Abstract: A method is described for the preparation of ACDA chemically bonded to silica gel as well as ACDA filter papers and their ion-exchange properties with metal ions have been investigated. The parameters such as effect of pH and effect of time on the extraction efficiency of metal ions using SG-ACDA were studied. The SG-ACDA show greater affinity for Ag(I), Hg(II) and Pd(II) (exchange capacities about 1 mmol/g) compared to other metal ions like Cu(II), Ni(II), Cd(II), Zn(II), Pt(IV) (0.2–0.6 mmol/g). The kinetics of ACDA functionalised silica-metal interactions have been found to be very rapid, the time for 90% uptake being 1–5 min.

Anion-exchange properties of ammonium salts immobilized on silica gel

Abstract: Die- Anionenaustausch-Eigenschaften der uber Alkylketten verschiedener Lange an Silicagel gebundenen Ammoniumsalze (I)-(IV) in wasriger Losung werden untersucht.

Determination of residues of synthetic pyrethroids in fruit and vegetables by gas-liquid and high-performance liquid chromatography

Abstract: A multi-residue method for the determination of synthetic pyrethroids in fruit and vegetables is presented. After extraction with hexane-acetone, the pyrethroids are separated from co-extractives by a partition process and chromatography on a silica gel column and quantitatively determined by electron-capture gas-liquid chromatography and/or high-performance liquid chromatography using an ultraviolet spectrophotometric detector.

Simple, low-cost method for determination of selected chlorinated pesticides in fat samples.

Abstract: A method is described for the quantitative and qualitative determination of selected chlorinated pesticides in fat samples. Pesticides residues are extracted with petroleum ether and separated from fat with concentrated H2SO4 instead of the commonly used adsorbents Florisil, alumina, or silica gel. Residues were analyzed by gas chromatography with electron capture detection. Recoveries of fortified samples were approximately 100%.

Adsorption from binary solvent mixtures onto silica gel by HPLC frontal analysis

Abstract: The chromatographic technique of frontal analysis is applied to measuring adsorption from binary liquid mixtures by silica gel. The complete adsorption isotherm of a solvent mixture is obtained by measuring the break-through curves for a series of small concentration steps of the mobile phase. This method offers a direct way to determine the composition of the stationary phase in liquid-solid chromatography with mixed mobile phases. The surface excess isotherms of all binary systems formed by benzene, cyclohexane, and 1,2-dichloroethane, at the solution-silica gel interface at 25 °C are presented. The data of the three systems are shown to be thermodynamically mutually consistent.

Process for producing ethylene glycol and/or glycolic acid ester, catalyst composition used therefor, and process for production thereof

Abstract: A hydrogenation catalyst composition useful for the hydrogenation of an oxalate diester, said composition being composed of a reduction product of copper-containing silica gel formed by contacting an ammine complex of copper with colloidal silica sol; and a process for producing the aforesaid composition Using a catalyst composed of the aforesaid composition, ethylene glycol and/or a glycolic acid ester can be produced from an oxalate diester efficiently with high conversions and selectivities and without causing pollution attributed to the use of a chromium-containing catalyst composition

Separation of carbohydrates by liquid chromatography on silica gel, adding adsorption modificators to the eluent

Abstract: For the separation of carbohydrates by liquid chromatography, utilizing the intermolecular interaction with amino groups on the surface of the adsorbent, two types of adsorbents were used: silica gel modified by adding to the eluent a diamine, and a chemically bonded phase prepared by the reaction of γ-aminopropyl triethoxy silane with silica gel. Mono- di- and trisaccharides could be separated on silica gel modified by the adsorption of piperazin and ethylene diamine from the eluent. The separation capacity of columns packed with silica gel with bonded NH2 groups and with silica gel having diamines adsorbed on its surface is similar. The retention volumes of 15 carbohydrates were measured on columns containing silica gel with hydroxylated surface and on silica gel modified with piperazin from the eluent consisting of acetone-water. Comparison of acetone-water and acetonitrile-water as the eluent showed that the former is also suitable for the analysis of carbohydrates.